Whole-body and regional basal lipolytic rates, the lipolytic response to exercise, and lipolytic sensitivity to epinephrine infusion will be determin-ed in obese and lean subjects by infusing (2H5) glycerol and (1-13C) palmitate in conjunction with abdominal vein catherterization and microdialysis probe insertion. Adipose tissue biopsies will be obtained to assess the molecular mechanisms regulating regional lipolysis.